As piezoelectric devices go, there are a gyro sensor for detecting an angular velocity, a piezoelectric vibrator and a piezoelectric oscillator that output a desired oscillation frequency, and a filter that selects a desired frequency band. A piezoelectric oscillator includes a package base having a recess portion therein. Onto this recess portion, a TAB tape is mounted, in which a wiring pattern to which an IC chip and a piezoelectric vibrating reed are connected is provided on the surface of an insulation tape. This TAB tape is constructed so that a window portion is provided for the insulation tape. A part of the wiring pattern is bent upward through this window portion. Further, on the lower surface of the TAB tape, the IC chip is mounted. The piezoelectric vibrating reed is mounted on the upward bent portion of the wiring pattern. Further, to the upper surface of the package base, a lid is joined, whereby the recess portion is air-tightly sealed (refer to, for example, FIG. 12 in Patent Document JP-A-2004-153408).
Further, if the piezoelectric device is a gyro sensor, the piezoelectric vibrating reed of the gyro sensor is H-shaped in plane. A base portion (mount portion) connected to a support body is provided in the center portion of the piezoelectric vibrating reed. From one end of this base portion, a pair of drive arms are protruded, and from the other end of the base portion opposed to the one end, a pair of detecting arms are protruded. For the drive arm, a drive electrode is provided, and for the detection arm, a detection electrode is provided. The drive electrode and detection electrode conduct to an electrode pad provided for the base portion (refer to, for example, Patent Document JP-A-2004-226181).
FIG. 8 is an explanatory view when the piezoelectric vibrating reed and the IC chip are mounted on the TAB tape. If a piezoelectric vibrating reed 1 having the mounted portion in its center portion is mounted on a TAB tape 2 through a bump, the TAB tape 2 must have a window portion 3 as disclosed in Patent Document JP-A-2004-153408 in the center portion of the TAB tape 2. If an IC chip 4 is mounted on this TAB tape 2, it cannot be mounted under the piezoelectric vibrating reed 1 because the window portion 3 is provided. Therefore, the TAB tape 2 is extended to the side, and the IC chip 4 is mounted on this extended portion. However, when an electronic apparatus on which the piezoelectric device is mounted is minaturized, it is necessary to reduce the thickness and the plane size of the piezoelectric device. Therefore, the plane size of the piezoelectric device becomes large and the miniaturization cannot be achieved, so that the mounted space of the piezoelectric device becomes large.
Further, if the gyro sensor in which the piezoelectric vibrating reed is mounted on the TAB tape, there is a possibility that the wiring pattern of the TAB tape and the base plate thereof resonate due to a bending vibration of the piezoelectric vibrating reed. Therefore, the TAB tape is designed so that resonation is not produced. Though a resonation design may be obtained by calculation, the calculation becomes very complicated if the IC chip is mounted on the TAB tape. As such, the accuracy of the calculation is lowered. Therefore, the wiring pattern and the base plate resonate due to the bending vibration of the piezoelectric vibrating reed.
Further, in the piezoelectric device, its package inside is air-tightly sealed in an atmosphere of a vacuum or an inert gas. As an airtight sealing method, a lid may be joined onto the upper surface of a package base having a seal hole on the bottom surface. Thereafter, the seal hole may be melt-sealed with a sealant while putting the package in a vacuum. FIG. 9 is an explanatory view of the seal hole provided in the package base. FIG. 9(a) is a schematic plan view showing the seal hole provided in the package base and a mount electrode, and FIG. 9(b) is a schematic side view. An external electrode 6 is provided on a rear surface of the package base 5, and a mount electrode 7 for mounting a TAB tape, and a piezoelectric vibrating reed, an IC chip, and a circuit pattern are formed on an inner bottom surface of the package base. Further, a seal hole 8 penetrates the package base 5 linearly, so that the package outside can be confirmed visually from the package inside. Therefore, the position of the seal hole 8 in the package base 5 is limited by the position of the external electrode 6 and strength of the package. Therefore, the seal hole 8 can be provided near the mount electrode 7. However, if a conductive adhesive is applied onto the mount electrode 7 and the TAB tape is mounted on the mount electrode 7, the conductive adhesive frequently flows out from the mount electrode 7 and flows into the seal hole 8. As a result, the conductive adhesive can flow through the seal hole 8 to the rear surface of the package base 5, which obstructs the joint between the sealant 9 and the package base 5 when the seal hole 8 is melt-sealed with the sealant 9.
In view of the above, it is desirable to provide a piezoelectric device in which miniaturization of its plane size is possible and the resonance design of a TAB tape is readily performed. Further, it is desirable to provide a piezoelectric device which can surely seal a seal hole.